Pneumatic tire

ABSTRACT

A tire mold is provided with a groove-like saw cut in an area of a tire molding surface which comes into contact with a side surface of a tire. The saw cut comprises a pair of circumferential saw cuts arranged to be spaced in a tire diametrical direction, a grid-like saw cut which is expanded between the pair of circumferential saw cuts, and a plurality of frame-like saw cuts which are dotted between the pair of circumferential saw cuts. The frame-like saw cuts fringe a closed area which is wider than a smooth area defined by the grid-like saw cut. The grid-like saw cut surrounds the frame-like saw cuts to prevent the frame-like saw cuts from coming into contact with each other. The frame-like saw cuts are coupled to each other via the grid-like saw cut.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/929,259, filed on Jun. 27, 2013 which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2012-225275, filed on Oct. 10, 2012, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a tire mold for cure molding a tire, amanufacturing method of a pneumatic tire by using the tire mold, and apneumatic tire.

Description of the Related Art

In cure molding of a tire, a tread surface and a side surface of anuncured tire are pressed to a tire molding surface of a tire mold, and aheating operation and a pressurizing operation are applied to theuncured tire. At this time, if an air lying between the tire moldingsurface and the tire creates an air accumulation without beingappropriately discharged, a notch-like recess is formed on an outersurface of the tire due to the air accumulation. The recess isrecognized as an area which is peeled or depressed along a tirecircumferential direction, and is particularly significantly created inthe side surface.

Generally, a vent hole serving as an exhaust hole is provided in an areaof the tire molding surface which comes into contact with the sidesurface of the tire. However, if a lot of vent holes are arranged, thenumber of rubber projections called as spews is increased incorrespondence to the vent holes, and there is a risk that an outerappearance of the tire is damaged by cut traces of the spews.Accordingly, it is not practical to increase the number of the ventholes for a countermeasure of the air accumulation.

On the contrary, as shown in FIG. 10, there can be thought a structurein which groove-like saw cuts 51 are provided in an area 50 of a tiremolding surface which comes into contact with a side surface of a tire,and the saw cuts are used as a flow channel for the air so as to enhancean exhaust efficiency. FIG. 10 shows an example in which the saw cuts 51extending in a tire diametrical direction are arranged in a tirecircumferential direction CD, and FIG. 11 shows an example in which sawcuts 52 inclined in relation to a tire diametrical direction, and sawcuts 53 intersecting the saw cuts 52 are arranged. However, there is acase that the air accumulation is still created, and it is known thatthere is room for improvement.

According to the knowledge of the inventor of the present invention, ithas been known that the rubber flows into the area 50 of the tiremolding surface from both an outside direction and an inside directionin the tire diametrical direction, and the air accumulation tends to becreated at a confluence position thereof. Particularly, in FIG. 10, therubber tends to flow in the tire diametrical direction, and the airaccumulation accordingly tends to be created. Further, in FIG. 11,although the rubber flowing direction is dispersed, the saw cut patternis uniform and a rubber motion flow is uniform. Therefore, there hasbeen a case that the air accumulation is still formed at the confluenceposition.

Each of Patent Documents 1-5 describes a tire which is provided withprojection-like ridges on a side surface, and it is assumed that sawcuts corresponding to the respective ridges are provided on a tiremolding surface of a tire mold for cure molding the tire. However, thetire molds do not suggest any means for solving the creation of the airaccumulation mentioned above.

PRIOR ART DOCUMENTS

Patent Document 1: Japanese Unexamined Patent Publication No. 2004-17828

Patent Document 2: Japanese Unexamined Patent Publication No.2008-137541

Patent Document 3: Japanese Unexamined Patent Publication No. 2011-37388

Patent Document 4: Japanese Unexamined Patent Publication No.2011-126335

Patent Document 5: Japanese Unexamined Patent Publication No.2012-106583

SUMMARY OF THE INVENTION

The present invention is made by taking the actual condition mentionedabove into consideration, and an object of the present invention is toprovide a tire mold which can inhibit a recess from being formed on anouter surface of a tire while preventing an air accumulation from beingcreated, a manufacturing method of a pneumatic tire which uses the tiremold, and a pneumatic tire.

The object can be achieved by the following present invention. Thepresent invention provides a tire mold provided with a groove-like sawcut in an area of a tire molding surface which comes into contact with aside surface of a tire. The saw cut comprises a pair of circumferentialsaw cuts which extend in a tire circumferential direction and arearranged so as to be spaced in a tire diametrical direction, a grid-likesaw cut which is constructed by a combination of saw cuts arranged indirections intersecting with each other and is expanded like a gridbetween the pair of circumferential saw cuts, and a plurality offrame-like saw cuts which are dotted between the pair of circumferentialsaw cuts and fringe a closed area which is wider than a smooth areadefined by the grid-like saw cut. The grid-like saw cut surrounds theframe-like saw cuts in such a manner as to prevent the frame-like sawcuts from coming into contact with each other, and the frame-like sawcuts are coupled to each other via the grid-like saw cut.

In the tire molding surface of the tire mold, since grid-like saw cutsexpanding between the pair of circumferential saw cuts are provided inan area which comes into contact with a side surface of the tire, therubber flowing direction is dispersed in comparison with the saw cutpattern as shown in FIG. 10. Further, since a plurality of frame-likesaw cuts are dotted between the pair of circumferential saw cuts, therubber tends to be stagnant locally in each of closed areas, and therubber flow is not uniform. Further, since the frame-like saw cuts donot come into contact with each other, the frame-like saw cuts do notform an obstacle to an expansion of the rubber over the tire moldingsurface. As a result, it is possible to prevent the air accumulationfrom being created by dispersing the air lying between the tire moldingsurface and the side surface of the tire, and it is possible to inhibitthe recess from being formed on the side surface of the tire which iscure molded by using the mold.

In the pneumatic tire in accordance with the present invention, it ispreferable that the frame-like saw cuts are coupled to the otherplurality of frame-like saw cuts by the grid-like saw cut, and a lengthof a line segment of the grid-like saw cut coupling the frame-like sawcuts is between once and triple a length in a longitudinal direction ofthe line segment of the closed area surrounded by the frame-like sawcuts. Accordingly, since a lot of frame-like saw cuts are dotted atappropriate intervals so as to apply a sufficient change to the rubberflow, it is possible to well prevent the air accumulation from beingcreated by efficiently dispersing the air.

In the pneumatic tire in accordance with the present invention, it ispreferable that a surface shape of the frame-like saw cut is formed as apolygonal shape having four or more sides or a circular shape.Accordingly, the flowing direction of the rubber which passes throughthe closed area can be easily dispersed, and the creation of the airaccumulation can be effectively prevented.

In the pneumatic tire in accordance with the present invention, it ispreferable that the closed area becomes smaller or larger toward aposition closer to an inner side in the tire diametrical direction. Inthis case, a preferable change can be applied to the flow of the rubberwithout deteriorating the fluidity of the rubber so much, by arrangingthe comparatively wide closed area in the side where the side surface ofthe tire is pressed to the tire molding surface in advance.

The present invention provides a manufacturing method of a pneumatictire comprising a step of carrying out cure molding by setting anuncured tire to the tire mold mentioned above, and pressing the sidesurface of the tire to the tire molding surface of the tire mold.According to the method, it is possible to inhibit the recess from beingformed on the side surface of the vulcanization molded tire, whilepreventing the air accumulation from being created by the saw cuts asmentioned above which are provided on the tire molding surface of thetire mold.

The present invention provides a pneumatic tire provided with aprojection-like ridge in a side surface. The ridge comprises a pair ofcircumferential ridges which extend in a tire circumferential directionand are arranged so as to be spaced in a tire diametrical direction, agrid-like ridge which is constructed by a combination of ridges arrangedin directions intersecting with each other and is expanded like a gridbetween the pair of circumferential ridges, and a plurality offrame-like ridges which are dotted between the pair of circumferentialridges and fringe a closed area which is wider than a smooth areadefined by the grid-like ridge. The grid-like ridge surrounds theframe-like ridges in such a manner as to prevent the frame-like ridgesfrom coming into contact with each other, and the frame-like ridges arecoupled to each other via the grid-like ridge. Since the saw cutscorresponding to the ridges as mentioned above are provided on the tiremolding surface of the tire mold to which the side surface of the tireis pressed, the creation of the air accumulation can be prevented asmentioned above at a time of the cure molding, and the formation of therecess on the side surface of the tire can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view schematically showing an example oftire mold according to the present invention;

FIG. 2 is a plan view as seen from an arrow A in FIG. 1;

FIG. 3 is a cross sectional view as seen from an arrow B-B in FIG. 2;

FIG. 4 is an enlarged view showing by extracting a part of saw cutsshown in FIG. 2;

FIG. 5 is a plan view of saw cuts according to the other embodiment ofthe present invention;

FIG. 6 is a plan view of saw cuts according to the other embodiment ofthe present invention;

FIG. 7 is a cross sectional view showing a state in which an uncuredtire is set to a tire mold;

FIG. 8 is a perspective view schematically showing an example of a curemolded pneumatic tire;

FIG. 9A is a view showing saw cuts according to Comparative Example 2;

FIG. 9B is a view showing saw cuts according to Comparative Example 3;

FIG. 10 is a view showing conventional saw cuts; and

FIG. 11 is a view showing conventional saw cuts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be explained with referenceto the drawings.

FIG. 1 shows a schematic cross sectional view of a tire mold TM(hereinafter, referred to as mold TM) serving as a tire curing metalmold. At a time of cure molding, an uncured tire (not shown) is set tothe mold TM while setting a tire axial direction up and down. The moldTM is provided with a tread mold portion M1 which molds a tread portionof the tire, and side mold portions M2 and M3 which mold side wallportions of the tire, and a tire molding surface 20 is constructed byinner surfaces 21 to 23 of the respective mold portions. Although notbeing illustrated, a concavo-convex shape corresponding to a treadpattern is formed in the inner surface 21 of the tread mold portion M1.

At a time of the cure molding, a tread surface of the tire is pressed tothe inner surface 21, and the side surfaces of the tire are pressed tothe inner surfaces 22 and 23. Groove-like saw cuts 10 are provided in anarea of the tire molding surface 20 coming into contact with the sidesurfaces of the tire, that is, the inner surfaces 22 and 23 of the sidemold portions M2 and M3. As shown in FIG. 2, the saw cut 10 includes apair of circumferential saw cuts 1 and 2 which extend in a tirecircumferential direction CD, a grid-like saw cut 5 which is constructedby a combination of saw cuts 3 and 4 arranged in an intersectingdirection with each other, and a plurality of frame-like saw cuts 6. Thesaw cut 10 may be provided only in one side in a tire width direction (avertical direction in FIG. 1).

The circumferential saw cuts 1 and 2 are arranged so as to be providedwith a distance P in a tire diametrical direction, and form an annularband-like area. A vent hole 24 is set in a saw cut 7 which iscommunicated with the circumferential saw cut 2, however, may be set inthe circumferential saw cuts 1 and 2 or in the band-like area. There isa case that a mark or a logo is displayed in the band-like area. Asshown in FIG. 3, the band-like area is formed so as to slightly protrudefrom the inner surface 23, and a protruding height H1 is, for example,between 0.3 and 0.6 mm. The band-like area may be formed on the samesurface as the inner surface 23 or a position which is concaved from theinner surface 23.

A depth D1 of the circumferential saw cut 1 on the basis of the innersurface 23 outside the band-like area is set, for example, between 0.5and 1.2 mm. A depth of the circumferential saw cut 2 is the same as theabove depth. The pair of circumferential saw cuts 1 and 2 are arrangedso as to have a tire maximum width position MP therebetween, and theband-like area is positioned approximately at the center of the tiremolding surface 20 in the tire diametrical direction, however, thecircumferential saw cuts 1 and 2 may be arranged in an inner side in thetire diametrical direction than the tire maximum width position MPwithout being limited to the above. The width of the band-like area,that is, the distance P of the circumferential saw cuts 1 and 2 which ismeasured in the tire diametrical direction is preferably equal to ormore than 15 mm, and is more preferably equal to or more than 25 mm.

As shown in FIG. 4 in an enlarged manner, the grid-like saw cut 5 isexpanded like a grid between the pair of circumferential saw cuts 1 and2 (that is, within the band-like area), and a smooth area 8 forming amesh of the grid is defined by the grid-like saw cut 5. Each of the sawcuts 3 and 4 constructing the grid-like saw cut 5 is inclined inrelation to the tire diametrical direction and extends in a direction ofcoupling the pair of circumferential saw cuts 1 and 2. An angle θ ofintersection between the saw cut 3 and the saw cut 4 is, for example,90±15 degrees. In the present embodiment, the saw cuts 3 and 4 areconstructed by a straight line; however, they can be constructed by acurve.

The frame-like saw cuts 6 are dotted between the pair of circumferentialsaw cuts 1 and 2 (that is, in the band-like area), and are provided at aplurality of positions in the tire circumferential direction CD and aplurality of positions in the tire diametrical direction over a wholeperiphery of the tire. The frame-like saw cut 6 has a quadrangularsurface shape which laps over the grid-like saw cut 5, opposite sidesthereof are constructed by a part of the saw cuts 3, and the otheropposite sides are constructed by a part of the saw cuts 4. A depth D2of the grid-like saw cut 5 and a depth D3 of the frame-like saw cut 6are, for example, between 0.15 and 0.7 mm, preferably between 0.2 and0.4 mm, and are smaller than the depth of the circumferential saw cuts 1and 2 on the basis of the surface of the band-like area.

The frame-like saw cut 6 fringes a closed area 9 which is wider than thesmooth area 8 defined by the grid-like saw cut 5. Accordingly, a lot ofquadrangular closed areas 9 which do not include any saw cut are dottedin the band-like area. In FIG. 2, in order to easily discriminate on thedrawing, the several closed areas 9 are colored with a dingy color. Thesurfaces of the smooth area 8 and the closed area 9 are formed smoothlyalong a curved surface of the band-like area; however, the surface mayprotrude in the closed area 9. An area of the closed area 9 is set, forexample, to twice to eight-fold an area of the smooth area 8.

In the saw cut 10, the grid-like saw cuts 5 surround the frame-like sawcut 6 so as to prevent the frame-like saw cuts 6 from coming intocontact with each other, and a plurality of smooth areas 8 areinterposed between the frame-like saw cuts 6. Further, the frame-likesaw cuts 6 are coupled to each other via the grid-like saw cuts 5. Inthe frame-like saw cuts 61 to 63 which are shown in FIG. 4 and do notcome into contact with each other, the frame-like saw cut 61 and theframe-like saw cut 62 are coupled via a plurality of saw cuts 3, and theframe-like saw cut 61 and the frame-like saw cut 63 are coupled via aplurality of saw cuts 4.

In the mold TM, since the grid-like saw cuts 5 are provided between thepair of circumferential saw cuts 1 and 2, it is possible to disperse therubber flowing direction in the band-like area at a time of curemolding. Further, since the rubber tends to be adhered in the closedarea 9 in comparison with the peripheral area thereof, the rubber tendsto stay locally here and there in the band-like area, and the flow ofthe rubber is not uniform. Further, since the frame-like saw cuts 6 donot come into contact with each other, this structure does not form anobstacle to expansion of the rubber over the band-like area. As aresult, it is possible to prevent the air accumulation from beingcreated by dispersing the air lying between the tire molding surface 20and the side surface of the tire. As mentioned above, the mold TMdisperses the air to such a degree that the air accumulation is notcreated, and does not aim at forcibly feeding the air to the vent hole.

The frame-like saw cut 6 is coupled to the other plurality of frame-likesaw cuts 6 by the grid-like saw cut 5. A length of a line segment of thegrid-like saw cut 5 coupling the frame-like saw cuts 6 is preferablybetween once and triple the length of the closed area 9 which issurrounded by the frame-like saw cuts 6, and the length of the closedarea 9 is measured in a longitudinal direction of the line segment.Since the rate is equal to or more than once, a rubber fluidity can besecured without approximating the closed areas 9 with each other morethan necessary. Further, since the rate is equal to or less than triple,the air can be effectively dispersed by appropriately approximating theclosed areas 9 with each other so as to apply a sufficient change to therubber flow.

Specifically, in FIG. 4, a length L3 of the line segment of the saw cut3 coupling the frame-like saw cuts 61 and 62 is set to be between onceand triple lengths L91 and L92 of the closed areas 9 which aresurrounded by the frame-like saw cuts 61 and 62. Each of the lengths L91and L92 is measured in a longitudinal direction of the line segment ofthe saw cut 3. In the same manner, a length L4 of a line segment of thesaw cut 4 coupling the frame-like saw cuts 61 and 63 is set to bebetween once and triple lengths L93 and L94 of the closed areas 9 whichare surrounded by the frame-like saw cuts 61 and 63. Each of the lengthsL93 and L94 is measured in a longitudinal direction of the line segmentof the saw cut 4.

Cross sectional shapes of the pair of circumferential saw cuts 1 and 2,the grid-like saw cut 5 and the frame-like saw cut 6 are notparticularly limited, but can employ various shapes. In the case thatthe cross sectional shapes are formed as a shape which is narrowed in adepth direction, for example, a triangular shape, a trapezoidal shape ora semicircular shape, the shape is preferable since the saw cut can beworked without creating any undercut. In the case that the crosssectional shape of the saw cut is triangular, a leading end thereof isdesirably formed by a small circular arc.

There is a case that small stripes extending in the tire circumferentialdirection CD are formed in the inner surfaces 22 and 23 of the side moldportions M2 and M3. The small stripes are formed by a machine work in adifferent step from a forming step of the saw cut 10, and haveirregularity, for example, between several microns and ten and severalmicrons. In the present embodiment, since the saw cuts 3 and 4constructing the grid-like saw cut 5 extend in the directionsrespectively intersecting the tire circumferential direction CD, the sawcuts 3 and 4 intersect the small stripes mentioned above, whereby a flowchannel of the air is increased.

The surface shape of the frame-like saw cut 6 is preferably formed as apolygonal shape having four or more sides or a circular shape.Accordingly, a direction of the rubber flow passing through the closedarea 9 tends to be dispersed, thereby effectively preventing the airaccumulation from being created. FIG. 5 shows an example which employs agrid-like saw cut 14 having a different layout from FIG. 2, and isstructured such that a quadrangular frame-like saw cut 15 surrounds aclosed area 16. The frame-like saw cut 15 extends in a direction whichintersects both saw cuts constructing the grid-like saw cut 14. FIG. 6shows an example which employs a grid-like saw cut 17 inclined inrelation to the tire diametrical direction, and is structured such thata circular frame-like saw cut 18 surrounds a closed area 19.

In the saw cut 10 in FIG. 2, the closer to the inner side in the tirediametrical direction the closed area 9 is positioned, the smallerlittle by little the closed area 9 is, and the same applies to FIGS. 5and 6. This is associated with a fact that the side surface of theuncured tire is pressed in advance in the outer side in the tirediametrical direction. A sufficient change can be applied to the flow ofthe rubber in the outer side in the tire diametrical direction which ispressed in advance, and the change applied to the flow of the rubberbecomes smaller in the inner side in the tire diametrical directionwhich is pressed behind time. Therefore, a preferable change can beapplied to the flow of the rubber without deteriorating the fluidity ofthe rubber so much. In the case that the side surface of the uncuredtire is pressed in advance in the inner side in the tire diametricaldirection, the closed area 9 may be made larger toward the positionscloser to the inner side in the tire diametrical direction.

The mold TM mentioned above is structured in the same manner as thenormal tire mold except the matter that the saw cut 10 as mentionedabove is provided in the area of the tire molding surface which comesinto contact with the side surface of the tire, and the conventionallyknown material, shape and structure can be applied to the presentinvention. Accordingly, for example, the tire molding surface 20 isconstructed by three mold portions in the present embodiment; however,the tire molding surface may be constructed by a pair of mold portionswhich are divided into two sections at the center of the treat portion,in place of the above.

Next, a description will be given of a manufacturing method of apneumatic tire according to the present invention. Since themanufacturing method can be carried out in the same manner as theconventional tire manufacturing steps except a step of cure molding thetire, a description will be given only of the cure molding step. Themanufacturing method of the pneumatic tire has a step of cure moldingthe tire by using the mold TM which is provided with the saw cut 10 asmentioned above in the area of the tire molding surface which comes intocontact with the side surface of the tire.

In the cure molding step, after setting an uncured tire GT before curemolding as shown in FIG. 7, the mold TM is clamped as shown in FIG. 1.Further, in a state in which the tread surface and the side surfaces ofthe tire GT are pressed to the tire molding surface 20, the cure moldingis carried out by applying a heating operation and a pressurizingoperation to the tire GT. At this time, it is possible to prevent theair accumulation from being created by dispersing the air lying betweenthe tire molding surface 20 (particularly the inner surfaces 22 and 23)and the side surfaces of the tire GT as mentioned above. As a result, itis possible to inhibit the recess from being formed due to the airaccumulation, in the side surfaces of the cure molded tire.

FIG. 8 shows a pneumatic tire PT which is manufactured through the curemolding step as mentioned above. The pneumatic tire PT is provided witha side wall portion 32 which extends to an outer side in a tirediametrical direction from a bead portion 31 which seats on a rim, and atread portion 33 which is connected to an outer end of the side wallportion 32 so as to construct the tread surface. The side surface of thetire PT is provided with a projection-like ridge 40 which protrudes outof an outer surface of the side wall portion 32. The tire PT has thesame structure as the normal pneumatic tire except the provision of theridge 40, and is provided in an inner portion thereof with a carcass anda belt which are not shown.

The ridge 40 includes a pair of circumferential ridges 41 and 42 whichextend in a tire circumferential direction and are arranged so as to bespaced in a tire diametrical direction, a grid-like ridge 45 which isconstructed by a combination of ridges arranged in directionsintersecting with each other, and expands like a grid between the pairof circumferential ridges 41 and 42, and a plurality of frame-likeridges 46 which are dotted between the pair of circumferential ridges 41and 42 and fringe a closed area 49 which is wider than a smooth areadefined by the grid-like ridge 45. Further, in the ridge 40, thegrid-like ridge 45 surrounds the frame-like ridge 46 in such a manner asto prevent the frame-like ridges 46 from coming into contact with eachother, and the frame-like ridges 46 are coupled to each other via thegrid-like ridge 45.

Since the ridge 40 is formed by transcription of the saw cut 10, aspecific aspect of the ridge 40 can be supposed from FIG. 2. In otherwords, the circumferential ridges 41 and 42, the grid-like ridge 45 andthe frame-like ridge 46 are respectively formed by the transcription ofthe circumferential saw cuts 1 and 2, the grid-like saw cut 5 and theframe-like saw cut 6, and the smooth area and the closed area correspondto the saw cut 10 in the same manner. In the tire PT, since the airaccumulation is prevented from being created at a time of the curemolding as mentioned above, the recess is inhibited from being formed inthe side surface.

The present invention is not limited to the embodiment mentioned above,but can be variously modified and changed within the scope of thepresent invention.

Examples

By inspecting cure molded tires 100 by 100, a case that one or moretires which is determined as a defect bonding in a recess of a sidesurface exists was evaluated as “yes”, and a case that no such tireexists was evaluated as “no”. The size of the tire provided forevaluation is 196/65R15, and the structures of the tire molds in therespective examples are common except the shapes of the saw cuts. FIG.9A shows an aspect of Comparative Example 2, and corresponds to anaspect obtained by adding the frame-like saw cut in FIG. 5 to the sawcut in FIG. 10. FIG. 9B shows an aspect of Comparative Example 3, andcorresponds to an aspect obtained by connecting the frame-like saw cutsin the tire circumferential direction in the saw cut pattern as shown inFIG. 2.

TABLE 1 Compar- Comparative Comparative ative Working Working Example 1Example 2 Example 3 Example 1 Example 2 saw cut FIG. 10 FIG. 9A FIG. 9BFIG. 5 FIG. 2 pattern defect yes yes yes no no bonding

As shown in Table 1, in Comparative Examples 1 to 3, the tire which wasdetermined to be as the defect bonding in the recess of the side surfacewas confirmed. It can be thought that the result was caused by the factthat in Comparative Examples 1 and 2, the effect of dispersing therubber flowing direction was absent or small, and in Comparative Example3, the rubber flow was blocked by the frame-like saw cuts which are incontact with each other. On the contrary, in Working Examples 1 and 2,no tire which is determined to be as the defect bonding in the recess ofthe side surface was confirmed.

What is claimed is:
 1. A pneumatic tire having a side surfacecomprising: a pair of circumferential ridges which extend in a tirecircumferential direction and are arranged so as to be spaced in a tirediametrical direction; a grid-shaped ridge which is constructed byintersecting ridges having first ridges and second ridges, the firstridges and the second ridges being straight lines that are inclinedrelative to the tire diametrical direction, the first ridges and secondridges extending in directions that contact the pair of circumferentialridges, the first ridges intersecting the second ridges to form agrid-shaped pattern between the pair of circumferential ridges, theintersecting ridges defining smooth areas having a smooth surfacebetween adjacent ones of the intersecting ridges in the grid-shapedpattern; and a plurality of framing ridges framing closed areas whichare dotted in a repeating pattern between the pair of circumferentialridges, each of the closed areas having a smooth surface and being widerthan each of the smooth areas in the grid-shaped pattern, the pluralityof framing ridges being a subset of the intersecting ridges in thegrid-shaped pattern, and wherein the grid-shaped ridge surrounds theplurality of framing ridges in such a manner as to prevent the pluralityof framing ridges from coming into contact with each other, and theplurality of framing ridges are coupled to each other via thegrid-shaped ridge.
 2. The pneumatic tire according to claim 1, wherein alength of a line segment of the grid-shaped ridge coupling the framingridges is between once and triple a length in a longitudinal directionof a line segment of the closed areas framed by the framing ridges. 3.The pneumatic tire according to claim 1, wherein a surface shape of eachof the closed areas is formed as a polygonal shape having four or moresides or having a circular shape.
 4. The pneumatic tire according toclaim 1, wherein each of the closed areas becomes smaller as a positionof each of the closed areas is arranged closer toward an inner side inthe tire diametrical direction.
 5. The pneumatic tire according to claim1, wherein each of the closed areas becomes larger as a position of eachof the closed areas is arranged closer toward an inner side in the tirediametrical direction.
 6. The pneumatic tire according to claim 1,wherein each of the closed areas has a quadrangular surface shape, witha pair of opposing sides of the quadrangular surface shape being formedby a portion of the first ridges and another pair of opposing sides ofthe quadrangular surface shape being formed by a portion of the secondridges.